CHICAGO - The Mets are at a tipping point. Not yet a season-on-the-brink, do-or-die, win-or-be-fired scenario. But serious enough that a few changes soon might need to be considered after this week's four-game sweep by the Cubs at Wrigley Field, which always has been an ivy-covered House of Horrors for this team.

We're not talking strictly about personnel here, even though Wilmer Flores continued to test the Mets' patience with a game-turning error in Thursday's excruciating 6-5 loss. Sometimes a mental check is in order, a bit of housecleaning upstairs.

David Wright, out indefinitely, is a ghost right now. Vic Black and Bobby Parnell have been in limbo for a while. If the Mets are going to pull out of this tailspin and convince us that the 13-3 start was no fluke, the remaining guts of this team must deliver on a more consistent basis.

Michael Cuddyer doesn't have to be an MVP candidate, but he's got to do better than a .656 OPS if he's hitting in the middle of this lineup.

"You continue to put your work in, you continue to grind," he said, "and the tide changes."

There is truth to that. But it's not automatic. Jonathon Niese was another Met who could have stepped up Thursday. Just 28, he's an eight-year veteran, which gives him a level of seniority on this pitching staff.

Niese entered the game with a 1.95 ERA and had allowed more than one earned run only once in six previous starts. So imagine how Terry Collins must have felt when the Mets staked him to a 5-1 lead and Niese gave it all back with his fifth-inning meltdown.

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Part of that was on Flores, who turned a nice backhanded stab into a costly throwing error.

It's old news that Flores is not a Gold Glove shortstop. Thursday's error was No. 8 in 35 games. The Mets are trying to make do. We all know this. But Niese didn't have to roll over.

The next three batters? Walk to Dexter Fowler, Anthony Rizzo's run-scoring single and an RBI single by Kris Bryant that tied the score at 5.

"Just nothing went right," Niese said. "It was kind of a mixture between everything: bad luck, bad pitches. Our offense did a great job, got us the lead. It's unfortunate that I gave it up."

Unfortunate? Missing your train is unfortunate. Forgetting to take an umbrella is, too. Spitting up a 5-1 lead for a team that just lost three straight and can't score more than three runs twice a month? That can't happen. Not if the Mets intend to be a playoff team. They need more than "unfortunate" right now.

We guarantee the manager would use more colorful words than "unfortunate" to describe what Niese did, but as frustrated as Collins was by the whole Wrigley fiasco, he refused to call out anybody. He did suggest, however, that it's time for a few of this team's veterans -- especially with Wright on the shelf -- to keep the Mets afloat.

"This is when the Michael Cuddyers and the [Daniel] Murphys, that's when these guys need to step up with all that leadership we talked about," Collins said. "This is the time when you need it most, because we're young.

"We're very young right now. And with these guys struggling a little bit, one of the things you'll see in situations like this is these guys thinking they're hurting the club. And we can't have that."

One of those guys is Flores, who should have left Chicago happy after a fourth-inning homer. Instead, he had to sleep on a tough error that could further erode his confidence.

The Mets started him at shortstop and used Ruben Tejada's superior glove at third because they don't want to move Flores around. Until they have to.

"We'll sit down and continue to discuss it," Collins said. "If people say we've got to make a change, we'll make a change."

But not yet. The Mets expect to have Juan Lagares back for Friday night's game at Citi Field, so that's a positive. Having the lowly Brewers in town helps. More lineup adjustments could be on the way. But it's up to these Mets, this group, to get back to winning again. Or else.

David Lennon, covering baseball for Newsday since 1995, is an award-winning columnist, a voter for baseball's Hall of Fame, a two-time APSE top 10 columnist and has covered six no-hitters, including two perfect games.